This invention relates in general to spray equipment for testing the performance of viscous materials for high pressure spray applications and, more particularly, to hydraulic spray equipment capable of reducing the sample size required for testing purposes while more accurately testing such materials by precisely simulating assembly plant conditions.
The standard method of testing the "sprayability" of viscous materials, such as polyvinylchloride sealants or polyurethanes, involves the use of high pressure airless spray equipment. Such equipment, however, generally requires that at least a five gallon sample of material be prepared in order to conduct the necessary testing. A significant portion of the material sample is also wasted during the purging which is required to clean the hoses and other components of the system. Because tens and sometimes hundreds of experimental samples must be tested when a new product is being developed, the large quantities of material samples which must be prepared add significantly to the product development costs and can create environmental disposal issues as well.
Another problem with the use of conventional high pressure airless spray equipment is the temperature, pressure and speed controls provided in these systems often lack the precision necessary to provide reliable test data. Maintaining the desired sample temperature is particularly problematic because even if the sample is provided at the desired temperature, it might travel ten to twenty feet through material lines before reaching the spray valve. Additionally, the system must be purged before the sample is tested. Thus, the temperature of the sample may change before it is actually tested. Although it is possible to control the temperature of the entire room containing the spray equipment, such an approach is costly and time consuming, particularly in those situations where material samples are tested by gathering data points at ten degree increments, such as between 50.degree. F. and 100.degree. F.
Temperature control can be improved somewhat in airless systems by providing a heat exchanger. However, adding such a component to the system would substantially increase the minimum sample size and the time required for sample testing. Likewise, it is generally undesirable to provide robots for speed control in standard airless systems because it would increase the required sample size.
Pressure control with standard airless equipment is also unsatisfactory. A pressure gauge on a conventional spray gun will indicate that actual spray pressure varies significantly over time. While this variance may eventually even out, it can significantly alter the results of a test to measure spray pattern width. Even for flow rate testing the results may not be very accurate unless a substantial amount of material is used.
Although low pressure testing might adequately test most fresh material samples, it is unacceptable as a testing method for aged materials. In particular, low pressure testing of aged materials fails to accurately predict such critical parameters as spray pattern width and spray delivery rate. Furthermore, test results from low pressure testing will not necessarily predict spray performance for high pressure applications.
Moreover, there is a need for spray equipment capable of accurately testing the sprayability of both fresh and aged materials for high pressure applications. Conventional spray testing equipment maintains relatively imprecise temperature and pressure control for the sample material and provides no robot speed control for the spraying action. Furthermore, a problem exists with conventional testing equipment in that a relatively large quantity of material, typically at least five gallons, is required as a sample in order to test for such important parameters as spray pattern width and spray delivery rate. Additionally, at least two of these five gallons of material are wasted purging a conventional system. Consequently, substantial amounts of time, storage space, and material are unnecessarily consumed to prepare, store, and test the samples.